The invention relates to fabrication of semiconductor devices, more particularly to the etching of shallow isolation trenches in monocrystalline silicon substrates.
The fabrication of trenches in semiconductor substrates of integrated circuit devices that have an aspect ratio (depth to width ratio) greater than 1 to 1 is useful in several areas of ULSI (ultra large scale integration) processing. Trench etch processing has become critical to the fabrication of state-of-art electronic devices exploiting three dimensional structural concepts such as trench capacitors, trench isolation, and trench transistors.
Currently, shallow trench isolation (STI) uses Cl.sub.2 /HBr reactive ion etching to form trenches in masked monocrystalline silicon substrates. The trenches most desirably have smooth planar trench walls that slope inwardly in order to avoid void formations in the materials used to fill the trenches. The trenches are normally filled using chemical vapor deposition refill operations. Desirably, the slope of the trench walls will be less than approximately 85 degrees to avoid void formations, and greater than 75 degrees to conserve area on the device. The trench wall slope is defined as the complementary angle of the angle between the trench wall and the horizontal flat trench floor.
As the semiconductor devices become more microminiturized, the isolation trenches have become smaller and more narrow. This microminiturization resulted in serious problems in controlling the trench wall slope and the planarity of the walls.
Various methods and etching apparatus are known for controlling the profile and shape of etched trenches in semiconductor bodies. U.S. Pat. No. 5,298,790 discloses an etching process wherein and etching mask, which includes a layer of polysilicon that will absorb non-vertically traveling ions, is provided to influence the resultant trench profile. U.S. Pat. No. 4,690,729 discloses a method for etching trenches in a silicon body wherein an enchant mask is provided that includes silicon oxides. During etching, the silicon oxides of the mask are deposited on the resultant trench side walls and influence the etching action. U.S. Pat. No. 4,855,017 discloses a method for etching trenches in a silicon body. In the method, material is selectively deposited on the trench side walls during etching by including various agents in the plasma that will react with the silicon and form etch products that deposit on the trench walls. These deposits influences the etching action of the plasma to form the desired trench profile. U.S. Pat. No. 5,707,486 discloses a plasma reactor for etching various materials. The reactor has an electrode structure that defines the plasma generating field.